1. Field of the Invention
The present invention relates generally to armor used for preventing the penetration of structures by projectiles. More specifically, the invention relates to an improved armor including a fiber grid having composite tiles retained in the grid that together provide overall support to the structure being protected while also improving the armor performance of each individual composite tile.
2. Background of the Invention
Armor systems have been known to include thick metal as a skin of a structure being protected. For example, military vehicles have, for several years, included a thick metal plate on their exterior in order to reduce the likelihood of projectile penetration. Such thick metal armor systems while effective can also be extremely heavy and, as such, cause problems relating to vehicle speed, fuel consumption and vehicle assembly.
In some cases, these metal armor systems have been replaced with lighter weight armor systems made from composite materials having reinforced fibers made of, for example, Kevlar, S-2 glass, graphite, or high molecular weight polyethylene. Such armor systems have utilized these multiple layers of composite materials in order to achieve reduced overall weight, and provide sufficient structural properties, while preserving the ability of the armor to provide protection against penetration. For example, some known systems include the use of Kevlar in combination with two outer plates surrounding such Kevlar. Illustrative of such a composite armor system is disclosed in U.S. Pat. No. 4,186,648.
Also, armor systems using ceramic plates in connection with a grid are well known in the art as capable of providing protection against penetrating high speed projectiles while providing a reduction in the overall weight of the armor system. The ceramic plates have been known to have convex surfaces. U.S. Pat. No. 6,826,996 discloses convex plates inserted into a honeycomb grid. Upon impact by a projectile into such ceramic plates, it has been known that managing the propagation of cracks from the impacted plate to an adjacent plate is critical.
The prior art grids are made of steel, fiber, or composite materials and are used in connection with holding ceramic plates inserted into openings formed by such grid structures. For example, U.S. Pat. No. 5,456,156 discloses a grid structure made of metal strips. The openings have been known to be either blind openings, opening only to one side of the grid, or, through holes, open to both sides of the grid. The openings of such grids have been shaped in many different forms including, for example, squares, triangles, and hexagons. The grid structure is usually designed with a material having an effective acoustic impedance lower than the ceramic plates in order to reduce the propagation of damaging stresses to adjacent ceramic plates.
In order to manage the propagation of such stresses, prior art armor systems have used auxiliary layers of laminate sheet material bonded to the front and the back of the grid structures. In some cases, only one laminate sheet has been bonded to either one of the front or the back of such grid structures. It has been known to make such laminate sheet material out of Kevlar. For example, U.S. Pat. No. 5,349,893 discloses a composite laminate sheet made of woven fiber in a resinous matrix. Such laminate sheet materials can be bonded to the grid structure with resins.
Illustrative of the prior art is U.S. Pat. No. 6,826,996 assigned to General Dynamics Land Systems, Inc. and Mofet Etzion Agricultural Cooperative Association Ltd. The '996 patent discloses a honeycomb grid structure having openings for receiving convex composite plates and a pair of preform sheets secured to both sides of the grid structure. The '996 patent discloses the honeycomb grid as made of material selected from the group consisting of stainless steel, aluminum, aramid sheet, fiber, or fabric.
Testing of such known armor systems having grid structures with composite inserts surrounded by preform sheets has revealed that the propagation of cracks and debris, created during impact, weakens the adjacent composite plates. The propagation of such cracks results from poorly designed grid structures failing to eliminate both crack propagation, debris, and stress wave propagation.